A Monte Carlo study on a 90 .deg. compton scattering imaging system by using MCNP simulations

A new 90 .deg. Compton scattering method for the inspection of luggage samples has been investigated. The algorithm of this system based on measurements of the single Compton scattered gamma rays was developed to reconstruct physical images of the objects. The algorithm was constructed to estimate the electron density and linear attenuation coefficients by using the responses of scattering detectors and a transmission detector. The overestimation and under-estimation problem in calculation of total and Compton attenuation coefficients can be overcame by iteration method and by using adjustment method with the response of the transmission detector. The reconstruction algorithm was verified and tested by a Monte Carlo simulation using MCNP Code. The test material was a 5x5x5 cm object made of some common materials such as polyethylene, epoxy, water, lucite, aluminum, steel, and brass, whose densities are in the range of 0.94 g/cm3 to 8.5 g/cm3. The gamma source used in the simulation was Cs-137 that emits 0.662 MeV-energy gamma rays. The images obtained from MCNP Code were close to the simulated objects. The relative errors of calculated values to the actual values were about from 0.5% to 10%. These results indicate that quantitative reconstruction can be obtained from measurements